There were greater benefits for those taking pills daily or weekly – rather than in monthly super-doses – and in people who were deficient in the first place.

One of the researchers, Prof Adrian Martineau, said: “Assuming a UK population of 65 million, and that 70% have at least one acute respiratory infection each year, then daily or weekly vitamin D supplements will mean 3.25 million fewer people would get at least one acute respiratory infection a year.”

They are recommended all year round for some people who get little sunlight on their skin, including people in care homes or those who cover up.

Image copyrightThinkstockImage caption Vitamin D is made naturally by people’s bodies – if they get plenty of sunlight

However, there is considerable debate about the importance of the latest study.

Prof Louis Levy, the head of nutrition science at PHE, said: “The evidence on vitamin D and infection is inconsistent and this study does not provide sufficient evidence to support recommending vitamin D for reducing the risk of respiratory tract infections.”

But Prof Martin Hewison, from the University of Birmingham and the Society for Endocrinology, said the findings were “striking”.

“I agree with the authors that this study supports a new indication for vitamin D beyond its established benefits for bone health,” he added.

And the research wing of the NHS, the National Institute for Health Research which funded the study, said the findings were “worthy of serious further debate”.

Ultimately, the researcher team at QMUL want vitamin D to be added to food like in the US where milk is fortified.

“By demonstrating this new benefit of vitamin D, our study strengthens the case for introducing food fortification to improve vitamin D levels in countries such as the UK where profound vitamin D deficiency is common.”